What nuclease cleaves pre-mRNA in the process of polyadenylation?

A transcript-specific cleavage by a large set of proteins is the first stage of eukaryotic pre-mRNA polyadenylation. The main participant of this reaction-endonuclease-has not been discovered until now. However, mammalian CPSF-30 and yeast Yth 1p proteins are known to be homologues to Drosophila Clipper (CLP) protein, which possesses endoribonucleolytic activity. In the N-terminal region, all three proteins contain five copies of the CCCH zinc finger motif associated with nucleolytic activity in the case of CLP. The literature data on these proteins are reviewed here. These data were shown not to contradict the hypothesis that CPSF-30 and its homologues are the actual nucleases that cleave pre-mRNA in the process of polyadenylation.